


Lunch Break

by orphan_account



Category: Undertale (Video Game)
Genre: Adult Frisk, F/M, Oral Sex, Skeleton Sex, if by plot you mean a gag, porn with little plot, reader is frisk but i refuse to write in first person, undyne will never speak to sans again tbh
Language: English
Status: Completed
Published: 2016-04-03
Updated: 2016-04-04
Packaged: 2018-05-30 23:04:40
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 3
Words: 3,633
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/6445864
Author URL: https://archiveofourown.org/users/orphan_account/pseuds/orphan_account
Summary: <blockquote class="userstuff">
              <p>Papyrus knows that Sans and Frisk are fighting, and he asks Undyne to help make them get along. Chapter one 'plot', chapter two is smut. Chapter three is sin.</p>
            </blockquote>





	1. Chapter 1

“UNDYNE, PLEASE. I CAN’T STAND HOW MUCH THEY FIGHT BUT THEY ALWAYS DODGE THE SUBJECT WHEN I BRING IT UP. YOU MUST HELP THEM!” Undyne rolled her eyes and set down her knife, letting Papyrus take over making sauce so she could fold her arms and lean her butt against the counter. She hunched her shoulders and pursed her lips as her head-fins flared. 

“Look Papyrus, it’s shit that they’re fighting but there’s really not much I can do about it. I’m not a therapist.”

“BUT THEY RESPECT YOU!”

“Frist respects me, maybe. Sans? Ha, he doesn’t respect anything.”

“UNTRUE, UNDYNE! MY BROTHER DEEPLY RESPECTS FRISK! ALSO ASGORE’S CLONE! ANYONE WHO MAKES BAD JOKES, REALLY,” Papyrus said indignantly. Undyne threw up her hands and groaned.

“My point still stands! What am I supposed to do to stop them from fighting?”

“JUST TALKING TO THEM WILL BE ENOUGH, I THINK.” Papyrus declared as he threw more vegetables into the pot. Undyne flared her fins again but didn’t bother mentioning that the sauce was just going to cook unevenly now. Papyrus turned on her with gleaming eye sockets, his teeth gnashing slightly in apprehension. “PLEASE, UNDYNE, TALK TO MY BROTHER AND FRISK!”

Undyne drew back her lips over rows of pointed, yellow teeth before she shrugged. “Fine. I’ll go now but if my house burns down again you’re rebuilding it this time,” Undyne warned. Papyrus cheered as Undyne stormed out of the house she shared with Alphys, turning sharply on her heel to wade through the snow to the house shared by Frisk and the skeletons. Her move to Snowdin had been reluctant, but now that she was here in a house identical to her last one she had found the location seemed pleasant. Aside from the fact that she now had less privacy than she had once enjoyed.

The front door to the brother’s house was unlocked, and Undyne let herself in without knocking. The inside of the house was dark, with a comfortable smell that relaxed Undyne enough that her fins lay flat. She had been expecting that Sans and Frisk would be eating lunch, that’s all Sans seemed to do since he had learned how well Toriel had taught Frisk to cook but there was no one at the table, just two untouched plates. 

Undyne frowned and rubbed the back of her head, confused and frustrated. Were they out? Well it would make things easier on her, at least. She was just about to turn around and walk back home when she heard a sudden scream. Sharp and loud, making Undyne’s fins perk up and stand on end followed by a sudden thump like something had been thrown across the room. 

In a moment Undyne’s spear had materialized in her hand and she charged up the stairs to Sans’ room. When Papyrus said fight she had imagined arguing not actual fighting! She wasn’t sure if she was worried more for Frisk or Sans, both could be dangerous if they wanted to. Still, Undyne would stop them before either of them could be harmed. 

Without breaking stride, Undyne slammed her whole weight into Sans’ door, throwing it off the hinges and sending it slamming into the room. She sprang in and landed on the collapsed door, her spear at the ready, “Cut it out!” she bellowed before she looked a little to the right and saw something she did not expect. 

On the top of the bed, lying on crumped blue sheets was Frisk, stark naked. They had propped themselves up on their elbow and were staring at Undyne with wide, confused eyes. Undyne’s jaw dropped. She had only seen naked humans in the cartoons Alphys watched but the real thing . . . round breasts flushed with a hint of red and plump hips with only a light hint of Frisk’s muscles. Undyne’s eyes were drawn to their body and she blushed a brilliant purple to match the scarlet of Frisk’s face. Sans was perched on the end of the bed, naked as well but his skeletal body was far less interesting. He had been stooped over and his glowing blue tongue lolled out of his mouth, dripping with something that was without a doubt not saliva. 

Sans’ eyes were empty sockets and after a long pause where Undyne was too horrified to move he made a low growling sound. “g e t o u t,” Sans said, and Undyne snapped out of her trance. She stumbled off the fallen door, picking it up and pulling it back so it fit in the frame, effectively closing it after her. Undyne stood on the other side for a moment before she managed to sputter, “Papyrus can hear you fucking.” 

“Oh god,” Frisk said. That was all Undyne caught before she turned and bolted out of the house.


	2. Sinners TBH

**Summary for the Chapter:**

> Sans bailed out on work to meet Frisk, set a little before chapter one.

**Notes for the Chapter:**

> OKAY LOOK. I did mean for this to be a two parter but I need to make a third chapter. 
> 
> Also, I know I used they/them pronouns for someone who's clearly female-bodied in text but c'mon you can't expect a lesbian to write porn without any boobs.

Frisk had been hard at work while Sans had been snoozing at his post, it seemed. When he teleported silently into the house he saw them working away, plating the meal they had made and wiping their hands off on their short, purple apron. He grinned and slipped into the kitchen, waiting until they set down the pan they had been handling before he slid behind them and put his hands around their hips. 

Frisk yelped and jumped slightly and Sans pulled their hips against his. “Sans!” Frisk protested, “shouldn’t you be at work?” 

“i’m on break,” Sans said casually. He pressed his face against the back of their neck and one hand trailed up to rub against the sharp bone of Frisk’s hip. Their breath hitched and Frisk pressed against Sans. 

“Well the table’s set already, I just have to finish making our tea-“ 

“actually, i was thinking we might have a little fun first.” Sans said. He slipped his hand into the front of their shorts and began to gently rub the cleft between their legs through their underwear, quickly finding their clit and gently rubbing either side of it. Frisk bucked slightly and laughed before they swatted his hand away playfully, slipping it out from their pants. 

Sans pouted as Frisk turned around to sit on the counter and faced him. “C’mon Sans, I worked really hard! Don’t you want even a little taste?” They leaned down and kissed his collar bone. Sans squeezed his eyes shut and suddenly turned Frisk’s soul blue. “Hey!” Frisk complained as they were suddenly lifted into the air. 

“what?” Sans asked innocently. He lifted them high into the air, making them drift along through the air as he meandered up to their shared bedroom. “it’ll be just as good after i taste you. probably better, even,” Sans winked as he unlocked his door with one hand before floating Frisk on in and dropping them on the bed. The room was neater since Frisk moved in, the bed was always usable and while his books littered the floor and spare hoodies were draped over his treadmill Frisk kept most of the carpet visible and regularly cleaned out the trash. It was more comfortable than it had been ever before, even if the bed was a little too small for two people.

“Oh let me up!” Sans chuckled as Frisk writhed, still pinned to the bed by their blue soul. He only gave them enough room to squirm and buck as he eased off his own hoodie and shirt, dropping them to the ground. His own soul burned a wild blue, reacting to excitement and stimulation. He could feel his magic molding into a pointed, gleaming tongue and he swiped it over his teeth to get a proper feel for it before he prowled forward with a predatory air. Frisk wiggled a bit as he climbed atop them, letting their soul turn red again but keeping them pinned with his knees on either side of their hips. 

Sans slid his hands under their shirt, feeling the soft plane of their stomach as he slipped it up and over their head, leaving it tangled around their elbows to prevent free movement. Their bra was plain green and a little too small so their even on their back Frisk’s breasts pressed into the fabric. Sans deftly opened it and pulled it fully away, freeing their chest completely. Sans bent and ran his tongue around their dark nipple, flicking at the end of it when it perked up as he cupped their breast in his other hand and teased that nipple between his thumb and forefinger. 

“Oh!” Frisk moaned. One hand grabbed the back of his skull, holding him so close Sans was sure he could feel their throbbing heart in his teeth. With their other hand, Frisk worked down Sans’ gym shorts, an effort made more daunting by the fact that the same magic that formed his tongue had created a very erect cock that throbbed with each beat of Frisk’s heart. 

Sans had seen human men in the magazines that sometimes fell into the dump, and he was far from impressed. Even fellow monsters seemed unimpressive though not for length or girth. His had strong ridges and a head that seemed (and may have been) perfectly crafted for rubbing their g-spot. His magic tended to react strongly to the stimulation that made Frisk scream, and he was more than okay with the idea that their lust had changed his member into their perfect, personal tool.  
When Frisk finally managed to work his shorts down to his thigh bones they began to stroke him rapidly, finally drawing his attention from their plump breasts. 

Sans groaned and started to grind against their hips as Frisk pumped away. They were good, and it didn’t help that he was already half mad. As they aive him a little squeeze, Sans suddenly straightened his back and grabbed a handful of Frisk’s dark hair before he came, shooting glowing blue sperm across their breasts and face. Frisk gasped and turned up their head as Sans pulled their hair, though judging from their smirk Frisk was rather pleased with how quickly they had managed to finish off Sans. 

He was still hard, it would take a hell of a lot more than that to finish Sans off completely and he slid off the bed, quickly twisting Frisk around so they were lying longways on the bed before he yanked off their shorts and panties deftly. He was glad they hadn’t bothered to wear tights, Frisk never liked when he tore them but the bones of Sans’ fingers were far too rough to avoid a hole here or there. Frisk let out a scream when Sans pressed his cock against their soaked pussy, brushing up against their clit with a quick flick but he didn’t plan to take a dip so soon. “bet i can make you forget your own name,” Sans said as he eased off them.

Sans sank to his knees, pressing boney fingers against either of Frisk’s thighs to keep them open as he leaned his head in and slid his tongue deep inside them. He could feel Frisk tighten and spasm around him as he swirled his tongue around in small circles, alternating between oh so slow and rapid seemingly at random. As spasm ran through one of Frisk’s legs and they arched their back against the bed, throwing their head back in a lustful scream. Sans withdrew his tongue and went to work gently sucking on their wet lips, working his way up from the base of their labia to their clit. He was skilled for a man with no lips and he was sure he could make them cum even faster than he had if his door had not suddenly flown off the hinges as an angry fish sprang into their room, completely ruining the mood.


	3. Snack on the Go

**Summary for the Chapter:**

> This is pretty much just porn I won't lie.

Sans was actually doing his best to work consistently, including staying awake, at his posts. He did feel bad, Undyne hadn’t spoken to him at all ever since she had walked in on him and Frisk, and Frisk said Undyne had gone out of her way to avoid them too. It seemed the only way to wriggle Frisk back into their friend’s good graces included him getting into her good graces too, which meant being attentive every time she happened to wander by. 

It was exhausting. It took everything in Sans not to wander off or fall asleep as he sat at his desk. He just wanted to go home and cuddle Frisk, though they had been reluctant to fuck ever since they found out Papyrus could hear them. Sans wasn’t overly bothered by that, they could always go into Sans’ lab behind the house, sure there was no bed but it seemed like fun to him . . .

Sans groaned loudly, staring up at the tree hanging overhead when he heard a gentle giggle and almost fell out of his chair. “frisk!” Sans said delightedly as he sat upright and leaned on the table, trying his best to look suave and flirty. 

“what can i do for you all the way out here, little human?” Sans asked and Frisk buried their face in their mittens and giggled again. They were bundled up snuggly in a heavy coat Toriel had made them and a very dark gray skirt. They looked adorable.

“I got bored at home. And, um, Alphys said that she was going to watch Mew Mew Three with Undyne so, um, I was thinking-“

“say no more,” Sans said as he raised one hand and turned his head away slightly. “no human coming through any time soon, huh? no one from snowdin comes here either, and doggo won’t be here for another two hours…” He winked at them and leaned back as Frisk climbed into his sentry station. They sat down, spreading their legs and resting their feet on the seat on either side of his boney hips. Frisk smiled and raised their shirt over their chest, not taking off their warm clothes but giving Sans a nice eyeful. 

Seemed that Frisk hadn’t bothered with wearing a bra at all, and with a quick jerk Sans grabbed their hips and sat them down in his lap. “you sure know what gets me going,” he said as he dick formed nice and fast, hard and large enough to poke out of the top of his shorts and bump against Frisk’s thigh. 

“It doesn’t take much to get you going,” Frisk teased. They brushed a thumb over the top of his cock, getting a smear of glowing ectoplasm precum on their thumb which they promptly popped into their mouth. 

“heh, sweetie, that’s no way to get me to take it slow,” Sans said as he finally pulled the top of their shirt and jacket up over their head. It was cold out, and a red flush immediately settled on their skin and their breath puffed in the frosty air. It was cold for someone with skin, apparently. But Sans knew how to get them nice and hot. 

Time for something a little rough. 

Quickly, Sans flipped Frisk around and doubled them over on his sentry table. He simply ripped open the back of their tights and panties without touching their skirt, roughly exposing their pussy. Frisk was already soaking wet, dripping down their thighs and steaming lightly in the frigid air. Sans smirked and stood, dropping his shorts and lining up with them for a moment.  
“oh frisky,” sans said, “i don’t think you were very clear with what you want.” He pressed the head of his cock against them, rubbing between their labia as he leaned forward to run his tongue behind their ear. 

Frisk jerked their hips back a little, trying to slip him in but Sans forced them back, roughly pinning them against the table to prevent movement. “no, no, sweetheart. tell your old pal sans what you want. you could beg for it too.” He rocked his own hips from side to side, separating their lips and stimulating them as one hand slipped around to give their breast a hard squeeze. “god damn you’re wet. you really wanna be fucked, huh? c’mon frisk, all you have to do is beg.”

“P-please,” Frisk gasped, struggling weakly to get him inside them.

“please? please what, sweetie?”

“Fuck me! Please!” Frisk almost shouted, and their voice turned into a scream as Sans roughly slid in and started to rock his hips back and forth. Frisk’s arms twitched as they tried to hold themselves up but Sans grabbed both their arms and pulled them back so Frisk’s bare chest was forced down to the table. He liked the way Frisk looked like this and he started to pound into them, encouraged as Frisk’s words deteriorated into garbled words of excitement. 

Frisk was soaked, and so tight around him that Sans was worried he might cum just from being so far in. He moaned in delight as he rocked his hips from side to side again, holding himself off as he continued to stimulate every inch of them. It felt like they were getting tighter somehow and Sans yanked them upright and sank his teeth into their shoulder, adding just enough stimulation that Frisk came hard. Their legs spasmed and their eyes rolled back in pleasure and the feeling of how fucking tight and wet they were around him made Sans cum with a throaty groan, fulling them up with so much of his magic that Frisk’s lower belly glow a dull blue. 

When Sans pulled out his cock glistened and their thighs were stained with a mix of fluids. Sans had so much more left in him, though, and while Frisk was still losing their mind in pleasure he flipped them over onto their back so they were resting heavily on the table. Sans let one of their legs slumped down against the wood while he slid their other leg over his shoulder. Frisk had a nice looking cream pie going on still dripping glowing plasm.  
Sans slid two fingers inside Frisk, rubbing at their already overstimulated insides as he leaned forward and started tracing their labia with his glowing tongue.

He could almost feel their pulse in their clit when he gave it a wide lick. When Sans closed his mouth around their loins and sucked gently Frisk suddenly bucked, moaning and tearing off their own skirt in their eagerness to get more body for Sans to touch. Sans sucked gently at their clit, flicking it with the end of his tongue as he slid a third finger inside Frisk before they came for a second time, this time soaking all of his face before he slouched back into his chair. 

“fuck frisk,” Sans said, “I’m going to walk home with ice on my face. people will talk, you know.” 

“Nothing untrue, I hope,” Frisk said. Their voice was weak, and their chest heaved. Sans laughed as he sat himself done on his chair so Frisk’s naked body lay before him in all its glory. Sans reached out and rested a hand on their lower belly, a little concerned with how bright the glow from their stomach was. He had been really pent up, apparently. 

Frisk put his hand on his and looked up, smiling at him faintly. Sans squeezed his cock with his free hand as he began to gently stroke himself. God damn Frisk looked so hot. Seeing them messed up was more than enough to make his dick beg to be stroked. “I have a better idea,” Frisk said and Sans paused as they slid off the table and sank to their knees. Frisk was tall enough that Sans had to sit up straight for once in his life but that was completely inconsequential when Frisk leaned forward and kissed the very tip.

“oooh,” Sans said as he put his hands on Frisks head, tangling his fingers in their hair as Frisk took him fully in their mouth. Hot and wet, just what Sans loved. Frisk pulled their head back sharply so only the head was in their mouth and they worked their lips around the hard magic phallus. Sans was a big fan of human lips, human skin, human touch. Frisk wrapped their hand around the base as they licked and kissed at the head, occasionally flicking their tongue along the underside to trace at the sensitive channels of magic. His magic was sweet and sensitive to their touches and when Frisk gave him an unexpectedly hard squeeze he gasped and lurched, glad he was already sitting down. “holy shit,” Sans gasped, “frisk!” 

He looked down at them as Frisk released him from their mouth. They smiled briefly at him before they slowly, mind meltingly slowly, began to run their tongue along the underside of his cock as their fingers fluttered at the top. It was the unfaltering eye contact that made Sans flush a vibrant blue, though. The feel of their eyes touching his soul that made his cock throb urgently. 

Sans came on their face, splattering glowing blue cum across their skin with a loud gasp. 

“Oh for fucks sake!” 

Sans and Frisk both scrambled suddenly, Frisk grabbing their jacket and frantically covered themselves same time as Sans jumped up, still lacking his shorts but his cock vanishing in a glimmer of blue magic. “undyne!” He said and he tried to give her a formal salute like he wasn’t half naked and she hadn’t just seen him cum on his lover’s face. 

Undyne curled her lips over her sharp, yellow teeth before she turned on her heel and stormed back to Snowdin, not bothering to tell them why she had stopped by. Sans slumped and groaned, fully aware that this would mean at least another few weeks of Undyne avoiding the pair of them.


End file.
